Differential-pressure-balancing mechanism.



e. H. GIBSON DIFFERENTIAL PRESSURE BALANCING MECHANISM.

APPLICATION FILED AUG-24. 1912.

1,191,415. Patented July 18; 1916.

I 1 4 SHEETS-SHEET 1- Y a Fla: 3 f (a421,

\\\\\\\\\\ ZR I ,Z 9 a A G. H. GIBSON. DIFFERENTIAL PRESSURE BALANCING MECHANISM.

Patented J111y'18, 1916. I

4 SHEETS-SHEET 2- APPLICATION FILED AUG.Z 4. I912.

- INVENTOR 44.; ATTORNEY.

G. H. GIBSON.

DIFFERENTIAL PRESSURE BALANCING MECHANISM.

APPLICATION FILED AUG-24, 1912. 1,191,415, Patented July 18, 1916.

4 SHEETS-SHEET 3- G.H.GIBSON.

DIFFERENTIAL PRESSURE BALANCING MECHANISM.

APPLICATION FILED AUG.24, I912.

- Patented-July 18, 1916.

FIG. 10.

IT I ES I y )9- y y w NESS v BY 7 v ATTORNEY GEORGE HERBERT GIBSON, OF MONTCLAIR, NEW JERSEY.

'DIFFERENTIAL-PIKESSUBE-BALANCING MECHANISM.

Specification of Letters Patent.

Application filed August 24, 1912 Serial No. 716,803.

To all whom it may concern Be it known that I, Gnonen H. GIBSON, a citizen of the United States of America, residing in Montclair, in the county of Essex and State of New Jersey, haveinvented a certain new and useful Improvement in Differential-Pressure-Balancing Mechanism, of which the following is a true and exact de-' scription, reference being had to the accompanying drawings, which form a part thereof. v

A main object of my present invention is to provide simple and effective apparatus for measuring the differential of two fluid pressures. This I accomplish by the novel means which I have devised for balancing the dif- 'fluid pressures.

ferential action on a diaphragm or diaphragms of the two fluid pressures 'by the action on a connected diaphragm of a fluid under a pressure which is varied to produce the desired balancing action and which pressure is therefore a measure of the differential between the first mentioned two My different pressure balancing mechanism referred to is of especial utility in determining fluid rates of flow by measuring the difference between the fluid pressures at two points in the conduit or weir chamberthroughwhich the flow takes place. In particular the mechanism is well adapted for determining the flow of a liquid over a weir, located in a closed chamber in which the pressure in the vapor spacethereof is variable. The rate of flow over such a weir is a function of the varying accumulation of 1 liquid on the supply side of the weir. I determine the latter in accordance with the present invention by measuringithe difierential between the hydrostatic pressure of the liquid at a determined level on the supply side of the weir, and the pressure in the vapof space of the weir chamber, and my in-' vention consists in part in the manner in Which I have combined the weir chamber and the differential pressure balancing apparatus. When my differential pressure apparatus is used to determine fluid rates to flow in the manner referred to, the balancing PIGSSHIG'IS, in general, a non-linear function of the rateof flow, and a further object of the invention is to provide slmple and effective apparatus adapted to be actuated by the balancing pressure and to furnish readmgs proportional to the rate of flow to be determined. 1

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention however, and the advantages possessed by it, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described formsin which my invention may be embodied.

Of the drawings, Figure 1 is an elevation partly in section of apparatus for measuring the flow of a liquid through a closed weir chamber. Fig. 2 is an elevation partly in section of a combined water heater and weir Patented July 18,1916. I

measuring apparatus. Fig. 3 is a sectional f elevation of a portion of the apparatus shown in Fig. 1 taken on a larger scale than Fig. 1. Fig. 4 is a sectional elevation of a modified form of a portion of the indicating apparatus shown in Fig. 1. Fig. 5 is a section taken on the line 55 of Fig. 4. Fig. 6 is an elevation partly in section of a portion of a modified form of indicating apparatus. Fig. 7 is a sectional elevation of a modified form of differential pressure balancing unechanism. Fig. 8 is an elevation of apparatus for measuring the flow of fluid through a conduit, and Figs. 9, 10, 11 and 12 are elevat ons partly in section, each illustrating a different modification of portions of the I apparatus shown in Fig. 1.

In the drawings and referring first to Figs. 1, 2'and 3, A represents a closed weir chamber divided intoinlet and outlet compartments A and A respectively, by a weir B formed with one or more discharge notches B at its upper edge. Such a weir chamber may be used for a'variety of purposes and an important use of such apparatus is in connection with a water heater,

as shown in Fig. 2, wherein C represents an open feed water-heater of well known type from which the water passes to the inlet compartment A" of the weir chamber through the part A C represents the steam supply pipe to the heater, and C the cold water supply pipe. A represents the discharge pipe leading from the outlet compartment A to a boller feed pump or other hot water consuming or utilizing device. C represents a pressure equalizing connection between the vapor spaces of the heater and the weir chamber. In so far as above described the apparatus disclosed involves no departure from the apparatus set forth and claimed in my prior Patent No. 1,015,556 granted Jan. 23, 1912. The apparatus disclosed hereindoes differ from that disclosed in my prior patent however, in the means employed for measuring the accumulation of water on the supply side of the weir.

As shown in Figs. 1, 2 and 3, the means employed for measuring the accumulation of water on the supply side of the weir comprises a chambered casing member D formed as shown of two cup shaped casing parts D and D secured together by bolts D? passing through the flanges D The member D is divided into two compartments or pressure chambers R and S by a flexible diaphragm E. This diaphragm is clamped at its margin'between the flanges D and has its central portion stiffened by the disks E. The disks E as shown are formed with transverse webs E which abut against stops D carried by the casing parts D and D to thereby limit the movements of the diaphragm E. The cup shaped part D is formed at its top with an aperture D which 1s closed by .a flexible diaphragm F. The

, diaphragm F is secured in place-by the apertured clamping plate D bolted to the casing part D. The diaphragm F is stifl'ened at its center by the disks F. The casing part D -is formed with an aperture D closed by a flexible diaphragm G which is stiffened centrally by disks G and is secured in place by a clamping member D The three diaphragms E, F and G are coaxial and are rigidly connected together by the axially disposed bolts H and I, passing through the diaphragms F and G respectively and tapped into central bosses formed on the adjacent disks E. The diaphragm F and G are equal in area and substantially smaller than the diaphragm E. The diaphragm E,

F and G may be made of rubber or other suitable material. The chamber A below the water level, and the chamber S are connected to the vapor space of the weir chamber. In the preferred form shown the connection between theweir chamber and cham-' ber comprisesa horizontal pipe section K passing through the side wall of the weir chamber, a vertical section K connected at its lower end to the casing part D, and a fitting K provided with removable plugs K through which the pipe sections K and K and particularly the former, may be cleaned from time to time. The connection between the compartment S and the vapor space of the weir chamber comprises a pipe section L extending between the casing part be kept full and running over bycondensation. For instance, as shown, a metallic body L connected to the weir chamber wall may be arranged so that-thewater of condensation collecting on it will drip into the member L. v

, With the apparatus described the chambers R and S, the piping K, K and L, and the member L will be filled with water at all times. The water in the chambers R and S and the external portions of the piping connected thereto will be maintained at approximately the external or room temperature, and will be practically unaffected in temperature by the temperature in the weir chamber. This has the advantage of minimizing errors in the indications of the apparatus due to changes in the temperature and consequently in the density of the water in the piplng, and moreover, avoids subjecting the differential balancing pressure mechanism and particularly the different diaphragms to high temperatures or to sudden changes in temperature. 7

The downward pressure on the diaphragm E of the water in the chamber R will be partly balanced by the upward pressure of the water in the chamber S, but there will be a resultant downward fluid pressure action on the diaphragm E which will be proportional to the distance between the surface levels of the water in the member L and the water on the supply side of the weir. With the apparatus disclosed, this variable downward thrust on the diaphragm E is resisted by the upward thrust on the diaphragm G of pressure fluid introduced into the chamber T formed beneath the dia phragm G by the clamping member D which is cup shaped.

In the apparatus shown in Fig. 1, the means employed for maintaining the proper fluid pressure in the balancing chamber T comprises a pipe M supplying a suitable pressure fluid as compressed air or water under pressure. This pipe is connected to a pipe M by the restricted orifice m formed in the disk M clamped between the adjacent ends of pipes M and M by the coupling nut M The pipe M is connected to the chamber T by branch pipe M and is also connected to the waste valve casing D which is located above and in line with the diaphragm stem H. The valve casing D is carried by a pair of arms D connected at their lower ends to the casing part D. A valve seat member D is secured in the lower end of the casing D and is formed with a port D adapted to be closed by the ,ball valve J. This valve is lifted'from its seat on an upward movement of the diaphragm by an extension H of the bolt H adapted to enter the pressure in the chamber T exceed the balancing pressure required, while any excess of pressure in the chamber T is revented by the lifting of the valve J 0 its seat, which occurs on any slight upward movement of the diaphragms. The resultant force tending to move the diaphragms downward comprises a variable component and a constant component. The variable component is proportional to the vertical distance it between the weir notch apex level of the weir and the surface level of the water on the supply side of the weir. The constant component comprises (a), an element corresponding to the action on the upper side of the diaphragm E of the head of water between the weir notch apex level and the top of the member L, (b) the difference between the upward fluid pressure acting on the diaphragm I and thedownward fluid pressure acting on the diaphragm G; and (c), the weight of the diaphragms and attached parts moving with them. The pres sure of the atmosphere on the upper Side of the diaphragm F also tends to 'move the diaphragms downward. This is exactly balanced however, by what I term the un measured component of the fluid pressure in the chamber T when that pressure is measured. as will ordinarily be the case, by a gage indicating, not absolute pressure, but absolute pressure minus atmospheric pres.- sure'. Since the diaphragms -F and G are of equal area, the pressure in the chamber T is independent of the varying pressure in the vapor space of the weir chamber.

, The pressure P in the balancing chamber T may thus be expressed by the equation where a and b are readily determined constants and k is the distance defined above. The rate of flow over the weir is a function of the quantity h which is well known for many different types of weirs and in any case may be determined by calculation or experiment. For instance, in the case of a weir formed with'one or more V notches the rate of flow will be substantially proportional to 7;,5/2. From the foregoing it is apparent that a suitably graduated pressure gage M showing the gage pressure in the chamber T will indicate the rate of flow over the weir, and an important advantage of my invention consists in the fact that the pressure per unit of area in the chamber T may be made many times greater than the differential per unit .of area of the fluid pressures acting on the diaphragm E. This permits the use of commercial types of pressure measuring instruments and insures substantial and positive differences in the readings obtained thereby as the differential pressure varies by small increments. There is a distinct advantage in so arranging the apparatus so that in the form shown, a substantial balancing pressure is maintained in the chamber T when little or no water is flowing over the Weir since this initial pressure minimizes errors and makes the operation of the apparatus positive when the rate of flow over the weir is small.

In general, the flow over the weir is not a linear function of the quantity 7:. and suitable rectifying provisions must be made to properly integrate and register the flow of the Weir, and are advantageously employed where a graphic record of the flowis made. A simple and desirable form of cooperating rectifying and recording provisions is shown in Fig. 1. These provisions comprise a U tube N having one leg connected at its top to the variable pressure pipe M by pipe N, and having its lower portion N variable in cross section as hereinafter explained. The other leg is open to the atmosphere at its top and, as, shown, comprises portions N and N each of constant cross section. The cross section of the lower portion N is advantageously made appreciably smaller der the conditions of use. The shape of the section N of the U tube is such that the mercury displaced from it and forced into the section N will be directly proportional to the rate of flow over the Weir, so that the latter will be indicated by the proportional scale affixed to the U tube portion N and of which N represents the zero line. The manner in which the section N must be shaped to roduce this result is determined by the fol owing considerations.

-The vertical distance X between the sur-- face levels of the mercury in the two legs of the 'U tube will be proportional to the balancing pressure P and may be expressed by the equation From the two equations given above, the

equation I X=d(a+bh) may be derived from which it follows that X,+X. .+.O=da+b h where b is a constant.

In forming the U tube the distance C is made equal to cla so that Since the sum of the components X and X is thus proportional to the quantity k, and the component X is proportional to the rate of flow over the weir, and since the vol-- ume of the part of the 'U tube section N" above the mercury level therein is proportional to X it follows that .the variable cross section given to the U tube section N depends upon the flow law of the weir and may be readily determined from the latter by methods well known to those skilled'in the art. I

While it is comparatively simple to closely approximate the desired cross sections of the different portions of the U- tube, I consider it desirable .in some cases, to make provisions for adjusting the volume of some portion of the U tube. For instance, as shpwn in Figs. 4 and 5, I may form a vertica wal of the tube section-N and separate this groove from the mercury space of the section by a flexible membrane N". This membrane is adapted to be flexed by the adjusting blocks N mounted in the groove N and the cotiperating screws N. A similar adjustment-in the volume of different portions of the U tube may be obtained by the use of screws N threaded through the wall of a portion of the. U tube as shown in Fig; 6.

roove in N in the inner surface of the.

With this arrangement the adjustment is effected by causing more or less of the screws to extend into the tube. In some cases also, it is desirable to automatically adjust the net cross section of some portion of-the U tube in response to variations in conditions which affect the law of flow over the weir. or through the conduit to which the U. tube pertains. For instance, in the: apparatus shown in Figs. 1 and 2 the amount of water flowing over the weir'for a given balancing pressure P increases as the temperature of water rises. To compensate for this, I may locate a flexible tube N within the U tube section N and connect this flexible tube to the vapor space of the weir chamber. With this arrangement a change in the temperature of the water passing through the weir chamber will mean, in general, a change in the pressure in the vapor space of the weir chamber and this, transmitted to the oval tube N will expand the latter and thereby decrease' the net cross sectional area of the U tube section N. This will result in increasing the rate of flow indicated by the apparatus for a given value of the balancing pressure P. Practically however, with the apparatus shown in Fig.1, the errors due to ordinary temperature variations are so slight as to be negligible and indeed the smallness of these errors is an advantageous characteristic of my invention.

, In the modified form of the diflerential pressure balancing mechanism shown in Fig. 7 the casing DA is divided into pressure chambers R, S and T, similar to chambers R, S and T of the construction first described by diaphragms E, F and G. In the construction shownin Fig. '1, however, the admission of pressure fluid to the balancing chamber T is controlled by the-valve JA attached to the diaphragms and opening and closing a port M formed in:the end of a chambered member M secured to the easing DA in line with the axesof the diaphragms. The pressure supply pipe M opens freely into the member M. In this form of apparatus however, the'escape of the pressure fluid from the balancing chamber T can take place only through the restricted vent orifice ma provided" in the outlet pipe I);

until the equilibrium is restored, whereupon the valve will again close the port. In this construction, as in that shown in Fig. 1-, the diaphragm actuated controlling valve is normally cracked to-an extent sufficient to With the arrangement shown: in Fig. 7 it'will be apparent that when the permit as rapid. a leakage through the port that imposed upon the diaphragms in .the

construction shown in Fig. 1 by the hydrostatic head due to the vertical distance between the top of the member L and the apex of the weir notch. As shown the tension of the spring D is adjusted by means of a member D in threaded engagen'lent with an extension of the collar D employed to secure the diaphragm F in place.

The arrangement shown in Fig. 7, in which the outlet from the balancing chamber 1s restricted and the admission of the .ment of Fig. 1 preferable however, to that shown in Fig. since, with the first de-' scrlbed arrangement, the sensitlveness of the differential pressure balancing apparatus is less affected by pressure fluctuations in the pressure supply pipe and by. unduly large movements of the dlaphragm actuated valve.

The differential pressure balancinginechanism hereinbefore described is obviously not limited to use in the relation illustrated by Fig. 1, but is capable of use for many different purposes.

One example of a modified use of this apparatus is illustrated in Fig. 8 wherein U represents a conduit for water, steam, compressed air or other fluid provided witha Venturi tube section U. In such a conduit, as is well known, the rate of flow of the fluid passing through the conduit will be a function of the difference in the pressure at a full diameter portion of the conduit and the pressure ata restricted portion U of the Venturi tube section. To determine the flow through the conduit with the differential pressure balancing mechanism of Fig. 1, I may connect the pipe K of such a differential pressure balancing mechanism as is' shown in Fig.1 to a full diameter portion of the conduit U and connect the pipe L to the restricted portion U of the Venturi tube section. The pressure maintained in the balancing chamber will then be a function of the rate of flow through the conduit.

In the modification shown in Fig. 9 the dilferential pressure balancing mechanism for determining the flow over a weir-located in a closed we r chamber is located within the weir chamber AA on the outlet side of the weir BA and comprises a hollow casing Z closed at its lower end by a diaphragm EA directly exposed on its under side to the pressure in the vapor space of the Weir chamber. The diaphragm EA forms the lower wall of a pressure chamber R a portion of the upper wall of which is formed by the smaller diaphragm FA, which is exposed on its upper side to the pressure of the atmosphere through the hollow casing part Z by which the casing member Z is secured to the wall of the weir chamber AA. The chamber R is connected to the supply side of the weir below the liquid surface level by the pipe KA. The balancing pressure chamber T comprises a cup shaped member Z and a diaphragm GA directly connected to the diaphragms EA and FA. The member Z is connected as shown, to the casing Z by arms Z Arranged within the casing member Z is a valve casing Z similar to the valve Casing D of Fig. 1 and containing a similar ball valve operated by the stem Z connected to the diaphragms. The valve casing Z may be connected to the balancing pressure chamber T and to the pressure supply pipe M, and to suitable indicating apparatus as are the valve casing D and balancing chamber T of Fig. 1.

Under some conditions it may be desirable to employ a balancing pressure which is less than that of the atmosphere. This may be desirable, for instance, where there is no air compressor or other source of fluid under pressure immediately available, or which it is desirable to employ, and it is convenient to connect the balancing chamber to a vacuum pump, inspirator, or other low pressure apparatus. One example of such an arrangement is shown in Fig. 10 where DB represents a pressure balancing mechanism which may be identical in construction with the device A shown in Fig. 1 except that the chambered member D in Fig. 1 is replaced by the clamping ring D, and the latter 1n turn is replaced by a chambered member D formed with an aperture at its upper end receiving the ported valve seat member D". The port D through the valve seat member, D, which is open to the atmosphere at its upper end, is controlled by a ball valve J as in Fig. 1. Mia represents a pipe leading from the balancing chamber T to the inspirator W, which as shown, receives fluid under pressure through the pipe 1V and is open to the atmosphere through the expanding nozzle-W The pipe MA 1ncludes. a restricted port MD and 1s con nected between said port and the balancing chamber to a U tube NA by a pipe N The U tube NA differs from the U tube N of Fig. 1 in that the zero line N of the cham-' change in position identical in shape with the specially shaped portion of the chamber N of Fig. 1. In the apparatus shown in Fig. 10 the lower of the two pressures to be differentiated is admitted to the chamber S and the high pressure is admitted to the chamber R.

The operation of the apparatus shown in Fig. 10 is analogous to that of the-apparatus shown in Fig. 1. The pressure of the chamber T will tend to decrease toward the vacuum maintained on the outlet side of the port in a when the valve J is seated and when the valve J is unseated, atmospheric air will enter the chamber T causing the pressure to rise therein. The pressure in the chamber T will thus be proportional to the differential of the pressures in chambers R and S.

A simple modification of the differential pressure balancing apparatus heretofore described is shown in Fig. '11, wherein three separate cup shaped casing members, each having its end closed by a diaphragm, are placed in line and have their parallel diaphragms connected by the axial stem Y. As shown, the end casings RA and SA, receiving respectively the higher and lower pressures to be differentiated, have their diaphragms r and s of equal size and facing one another. The casing TA receiving the balancing pressure has its diaphragm 25 facing the diaphragm s, and is formed with a central valve seated port 25 controlled by the valve member Y adjustably secured to the stem Y which passes loosely through the port If. As shown, a vacuum pipe MA, having a restricted port ma, is connected to the interior of the casing TA. The operation of the apparatus shown in Fig. 11 is similar to that of the apparatus shown in Fig. ,10. It will be understood, of course, that by arranging the valve member Y within the chamher TA, the apparatus can be arranged to operate with a balancing pressure above that of the atmosphere in which case the higher pressure should be admitted to casing SA and the lower to casing RA.

The modification illustrated in Fig. 12 differs from the apparatus shown in Fig. 1 in that the pipe KK replacing the pipe K and K of Fig. 1 opens into the chamber S of the casing member D, while the receptacle L is located at an appreciably higher level than the inlet end of the pipe 'KK, and the pipe LL leading from the receptacle D, and .differs further in that the specially shaped portion N of the U tube is inverted. With this form of apparatus as in that shown in Fig. 1, a substantial balancing pressure will be required in the chamber T at all times. With the arrangement shown in Fig. 12, unlike that shown in Fig. 1, however, the balancing pressure required will dec ease as the rate of flow over the weir increases. In other words, the general law for the pressure in the balancing chamber may be expressed by the equation P:a|bh, where b is a constant negative quantity which can be determined just as the quantity 2) in the equation P:a+b'h These connections, therefore, do not require stuffing box or the like leakage preventing provisions which, if used, give rise to friction interfering with the free functioning of the apparatus. It will be apparent moreover that with all of the forms of the differential pressure balancing mechanism disclosed, it is possible, by varying the relative sizes of the diaphragms to obtain a balancing pressure which may be larger or smaller per unit of area as desired, than the differential of the pressures differentiated. Furthermore, the functioning of the apparatus is in nowise affected by changes in the absolute pressures to be differentiated, .but is solely responsive to the difference between these absolute pressures.

While in accordance with the statutes 1 have illustrated and described the best forms of apparatus now known to me, it will be apparent. to those skilled in the art that changes may be made in the form of apparatus disclosed Without departing from the spirit of my invention-and'that certain features of. my invention are useful for many purposes other than in connection with flow measuring apparatus.

Having now described my invention what I claim as new and desire to secure by Letters Patent is:

1. In a differential pressure balancing devicethe combination of an inclosure forming two differential pressure chambers separated by a common flexible wall and a balancing chamber separated from one of said pressure chambers by a flexible wall, the other of said pressure chambers having a flexible wall externally exposed to the atmosphere, means mechanically connecting all of said flexible walls together for simultaneous movement, and means responsive to the movements of said flexible Walls for maintaining a pressure Within said balancmg chamber tending to hold said flexible walls in a neutral position.

2. A differential pressurebalancing mechanism comprising in combination an inclosure forming two differential pressure chambers, each having a flexible Wall. portion and a: balancing chamber having a flexible wall portion and a vent connection, means mechanically connecting all of said flexible wall portions together for simultaneous movements, and means responsive to the movements of said flexible wall portions for regulating the pressure in said balancing chamber, comprising a pressure supply conduit connected to said balancing chamber by a restricted port, and a valve connected to said diaphragm and controlling said vent connection.

3. A differential pressure balancing device comprising a casing formed with an aperture in its wall, a flexible diaphragm closing-said aperture, two diaphragms parallel to the first mentioned diaphragm and dividing the interior of said casing into three pressure chambers of which the one remote from said aperture contains pressure fluid for balancing the differential action on said central diaphragm of the pressures in the other two chambers, means connecting said diaphragms for simultaneous movement, and means controlled by the movements of said diaphragms for regu lating the pressure in said balancing chamber.

.4. A difl'erential pressure balancing device comprising a casing formed with apertures in its opposite walls, a flexible diaphragm closing each aperture. :1 third flexible diaphragm parallel to the first mentioned diaphragms and dividing the interior of said easing into two pressuri chambers, means connecting said diaphragms for simultaneous movement and means for balancing the difl'ercntial action on said diaphragm of the pressures in said two chambers. i 5. In a differential pressure balancing device, the combination of an inclosure forming a pressure chamber, two parallel flexible walls acted on internally of the chama balancing pressure in said balancing chamber.

6. In a differential pressure balancing device the combination of an inclosure forming a pressure chamber, two parallel flexible Walls acted on internally of said chamber by one of the pressures to be differentiated and externally exposed, one to the pressure of the atmosphere and the in area and smaller than the other flexible wall mentioned.

7. A differential pressure balancing device comprising a casing formed with an aperture in its wall, a flexible diaphragm closing said aperture, two diaphragms par allel to the first mentioned diaphragm and dividing the interior of said easing .into three pressure chambers of which the one remote from the. first mentioned diaphragm receives pressure fluid for balancing the differential action on the central diaphragm of the fluidpressures in the; other two chambers, means connecting said diaphragms for sinulltancous movement, and means controlled by the said diaphragm for regulating the pressure in said balancing chamber and comprising a valve actuated by the movements of said diaphragms. a port admitting pressure fluid tosaid balancing chamber an 1 a vent port through which pressure fluid may escape from said balancing chamber, one of said ports being restricted and the other being controlled by said valve.

8. A differential pressure balancing device comprising a casing formed with an aperture in its wall, a flexible'diapln'agm closing said aperture, two diaphragms parallel to the first mentioned diaphragm fluid for balancing the differential action on the central diaphragm of the fluid pressure in the other chambers, the outer diaphragms being of equal area and smaller than said central diaphragm, means for connecting said diaphragms for simultaneous movement. and means connected to said diaphragms for regulating the pressure in said balancing chamber and comprising a valve'actuatcd by movements ofsaid diaphragms, a tconduit forming a port admitting pressure fluid to said balancing chamber, and a conduit forming a vent port through which pressure fluid may escape from said balancing chamber, one of said p )rts being restricted and the 7 other being controlled by said valve.

'9; A diflerential pressure balancing device comprising a caslng formed withan aperture in its wall, a flexible diaphragm closing said aperture, two diaphragms parallel j to the first mentioned diaphragm and dividing said casing into three pressure chambers of which the one remote from the first mentioned diaphragm receives pressure fluid for balancing the differential action on the central diaphragm of the fluid pressures in the other chambers, the outer diaphragms being of equal area and smaller than said central diaphragm,- means for connecting said diaphragm for simultaneous movement, and means connected to said diaphragm for regulating the pressures in said balancing chamber and comprising a valve casing formed with a port, a ball valve tending to seat on and close said port and a member connected to said diaphragms and adapted to engage said valve and move it off its seat on a predetermined movement of the diaphragms.

10. The combination with a closed Weir chamber, of apparatus for measuring the differential between the pressure in the vapor space of the weir chamber and the hydrostatic pressure in the weir chamber on the. supply side of the weir at-the lowest level at which flow over the weir occurs, said apparatus including a movable member, means for subjecting said member to a variable force which 1s a function of said pressure differential, and means for subjecting said member to a constant loading force.

11. The combination with a closed weir chamber and a weir therein, of means for measuring the flow of a liquid over the weir, comprising an inclosure -forming two pressure chambers, a pipe connection between oneof sald chambers and the weir chamber opening to the latter on the supply side of the weir below the lowest level at which flow over the war occurs, a pipe connection between the second pressure chamber and the vapor space of the Weir chamber, and a movable member acted upon in opposite directlons by the liquid pressures in the two pressure chambers, said weir chamber, pipe con nection and pressure chambers-being so relatively arranged that each pipe connection and pressure chamber will be normally filled with the liquid flowing over the Weir, and when'the liquid level on the supply side of the weir is at said lowest level, a resultant liquid pressure will be exerted on said movable member which will increase without changing in directibn when the height of liquid level on the supply side of the weir rises above said lowest level.

12. The combination with a closed Weir chamber, of means for measuring the flow of a liquid over the Weir comprising a differential pressure measuring device including an inclosure forming two pressure chambers separated by a flexible diaphragm, a conduit connecting one of said chambers to the weir chamber on the supply side of the Weir below the lowest level of flow, over the weir, and a second conduit leading from the other chamber to the vapor space of the weir chamber and opening upward thereln in the latter at a level below that at whlch the first mentioned conduit opens to the weir chamber.

' 13. The combination with a closed weir chamber, of means for measuring the flow of: a liquid over the weir comprisinga dlilerential pressure measuring device including an inclosure forming two pressure chambers separated by a flexible diaphragm, a condu t connecting one of said chambers to the weir chamber on the supply side of the weir below the lowest level of flow over the weir,

the pressure 1n one of said chambers, a second exposed to the pressure in another of said chambers and the third exposed to the pressure in the third of said chambers, an axially extending connection between sald diaphragms, and means for regulating the pressure in said balancing chamber and ncluding a valve mechanism controlled by the movements of said diaphragms.

15. In apparatus for measuring a quantity which is a non-linear function of the difierences between two pressures, the combination of a difi'erential pressure balancing mechanism comprising a balancing chamber formed with a flexible Wall, means sub ect ing said wall to an inwardly acting force consisting of a constant loading component and a component proportional to the differential of said pressures, means controlled by the movement of said flexible wall for maintaining a balancing pressure within said chamber, and a U tube having the end of one leg connected to said balancing chamber and adapted to contain a fluid body forming a liquid seal between the ends of said tube, the latter having the internal cross section of its legs so proportioned relatively be directly proportional to said quantity.

16. Pressure measuring apparatus com- I prising in combination a U tube adapted to contain a liquid sealing said tube and adapt ed to have one end connected to a source of pressure which is equal to a constant plus 'a nonlinear function of a quantity to be determined, and having the other end open to the atmosphere said tube having the internal cross section of its legs so proportioned relative to each other and to said function that the vertical distance between the liquid level in one of said legs and a predetermined zero level will be directly proportional to said quantity.

17. A vice comprising in combination a U tube internally exposed at its opposite ends to the pressures to be differentiated and adapted to contain a fluid forming a movable seal between the ends of the tube, manually adjustable means for varying the volume of a portion of said tube and a flattened flexible tube inserted in a portion of said U tube and adapted to receive a fluid pressure changing the shape of said flattened tube whereby the volume of the portion of the U tube receiving said flattened tube is varied when the internal pressure in the latter is varied.

18. A differential pressure indicating device comprising in combination a, member formed with a channel adapted tobe exposed at its opposite ends to the pressures to be diiferentiated and adapted to contain a fluid forming a movable seal between the ends of said channel and means for adjusting the cross sectional area of the portion of said channel through which one end of said seal moves as the differential of said pressures increases and diminishes.

19. A differential pressure indicating apparatus comprising in combination amember formed with a channel adapted to be exposed at its oppositeends to the pressures to be differentiated and adapted to contain a fluid forming a movable'seal between the ends of said channel and means for adjusting the cross sectional area of the portion of said channel through which one end of posed at its opposite ends 'to the pressures to be diflerentiated and adapted to contain a fluid forming a movable seal'between the ends of said channel and means for adjustdiflerential pressure indicating de- I ing the'cross sectional area of a portion of sa1d channel, said means comprising a flattened flexible tube extending into said channel and subjected to an internal pressure forming a movable seal between the ends.

of said channel, and means for adjusting said flexible wall portion at various points along the length of said channel to ad ust the cross sectional area of correspondmg portions of said channel.

22. A difl'erential pressure indicating device comprising in combination a member formed with a channel adapted to be exposed at its opposite ends to the pressures to be differentiated and adapted to contain a fluid forming a movable seal between the ends of said channel, means for manually adjusting the volume of a portion of said channel, and means for adjusting the vol ume of a portion of said channel in response to changes in a variable pressure comprismg a flexible wall exposed on one side to sa1d channel along a portion of the length of the latter and exposed on the other s1de to sa1d variable pressure.

23. A difl'erential pressure indicating de vice comprising a member formed wlth a channel adapted to be exposed at 1ts opposite ends to pressures to be differentiated and adapted to contain a fluid forming a mov-' able seal between ends of said channel, means for adjusting the volume of a portion of said channel in response to changes in a variable pressure comprising a flexible wall exposed on one side of said channel along a portion of the length of the latter and exposed on the other side to said varlable pressure.

24. The combination with a closed weir chamber, of means for measuring the flow of ential pressure measuring device including 1 an inclosure forming two pressure chambers separated by a flexible diaphragm, a

conduit connecting one of said chambers tov the weir chamber on the supply side of the weir below the lowest level of flow over the weir, and a second conduit leading from the other chamber to the vapor space of the we1r chamber and opening upward therein in the latter at a level different from that at which the first mentioned conduit opens to the weir chamber.

25. The combination with a closed weir chamber, of means for measuring the flow of a liquid over the weir comprising a d1f- 3 ferential pressure measuring device inlevel different from that at which the first 10 eluding an inclosur'e forming two pressure mentioned conduit opens to the weir chamchambers separated by a flexi'ble diaphragm, her and means for constantly supplying 'a conduit connecting one of said chambers liquid to said second conduit. to the weirchamber on the supply side of GEORGE HERBERT GIBSON the weir below the lowest level of flow over the weir, a second conduit leading from the Witnesses:

other chamber to the vapor space of the weir J RALPH GIBSON, chamber and opening upward therein at a EUGENE L. LARKIN'. 

